A wireless transmission device in a wireless communication system includes an amplifier that amplifies the power of a transmission signal. In the wireless transmission device, the amplifier is typically operated in the vicinity of a saturation area of the amplifier in order to increase power efficiency of the amplifier. However, when the amplifier is operated in the vicinity of the saturation area, a non-linear distortion is increased. Therefore, the wireless transmission device includes a distortion compensation device that compensates such a non-linear distortion in order to suppress the non-linear distortion and reduce the adjacent channel leakage ratio (ACLR).
One of the distortion compensation schemes used for the distortion compensation device is referred to as a “predistortion (hereinafter may be referred to as “PD”) scheme”. The distortion compensation device of the PD scheme suppresses a distortion of output of the amplifier by multiplying, in advance, a transmission baseband signal before input to the amplifier by a distortion compensation coefficient that has the reverse characteristic of the non-linear distortion of the amplifier and increases the linearity of the output of the amplifier. The signal that has been obtained by multiplying the transmission baseband signal by the distortion compensation coefficient through the multiplier may be referred to as a “PD signal”. Therefore, the PD signal is a signal that has been distorted in advance in accordance with the reverse characteristic of the non-linear distortion of the amplifier before the signal is input to the amplifier.
For example, as in the distortion compensation device of the PD scheme in the related art, there is a device including a table that stores a plurality of distortion compensation coefficients, and reads, from the table, a distortion compensation coefficient corresponding to an address value in accordance with the power of a transmission baseband signal. In addition, the distortion compensation device adjusts the read distortion compensation coefficient using an “adjustment coefficient”, and outputs the adjusted distortion compensation coefficient to the multiplier. In addition, the distortion compensation device performs feedback of a part of an output signal of the amplifier in the wireless transmission device, and detects, from the “feedback signal”, a “distortion component” that appears outside the “transmission band (that is, a channel)” applied to the wireless transmission device. In addition, the distortion compensation device may adjust distortion compensation processing (for example, “correct (update) the above-described adjustment coefficient”), based on the detected “distortion component outside the transmission band”.
Japanese Laid-open Patent Publication No. 2009-303225 is the related art.